Embodiments of the invention generally relate to a method and system for controlling a motor, and more particularly to a method and system for controlling an alternating current (AC) motor outputting a motor torque changing linearly with respect to a voltage phase angle of a voltage vector applied thereto.
An AC motor is controlled by a voltage vector outputted from a control system and generates a motor torque for driving wheels of a hybrid vehicle or an electric vehicle. The voltage vector is generated through converting a direct current (DC) voltage from a DC power source. The motor torque changes with a voltage amplitude and a voltage phase angle of the voltage vector. Currently, the motor torque is controlled through regulating both the voltage amplitude and the voltage phase angle. However, it's difficult to determine a good point of the voltage amplitude and the voltage phase angle to ensure that the motor torque is as high as possible to ensure the DC bus voltage utilization rate.
For example, an approach to improve the motor torque and the DC bus voltage utilization rate comprises fixing the voltage amplitude and varying the voltage phase angle so that the motor torque is controlled only through changing the voltage phase angle. For example, see Hideo Nakai et al., “Development and testing of the torque control for the permanent-magnet synchronous motor,” in IEEE Transactions on Industrial Electronics, Vol. 52, No. 3, June 2005. However, in this approach, the motor torque changes nonlinearly with the voltage phase angle. A shortcoming of this approach is that it cannot quickly and continuously calculate and control the motor torque.
It is desirable to provide a method and system for controlling a motor to address at least some of the above-mentioned problems.